Formats supported by DPL6 can be found here:
https://userguides.dxo.com/photolab/en/overview/#compatible_file_formats
Regarding Adobe DNG files:
DNG files created with Adobe Lightroom, Camera Raw or DNG Converter are supported as long as the native Raw files of the shooting camera are compatible with DxO PhotoLab. In DxO PhotoLab, DNG files created with Adobe software are considered Raw files. Therefore, all the tools and corrections specific to Raw files, as described in this user guide, also apply to DNGs.